Highly fluorinated model compounds for matter-wave interferometry

In order to explore the quantum-to-classical transition, the ambition of this thesis was the design and synthesis of tailor-made molecules for matter-wave interference experiments. Firstly, the focus was set on a deeper understanding of the influence of a molecule’s internal structure, especially its polarizability, on quantum interference. Furthermore, the limits of quantum mechanics were addressed by increasing the size of the interfering objects. The metrological aspect of molecule interferometry - to measure influences of molecule properties on the wave nature - is described in the first part of this thesis. Two fourfold perfluorohexyl functionalized constitutional isomers were synthesized in order to demonstrate that different molecular conformations can be distinguished in quantum interference experiments. A tetrahedral isomer and a rod-like oligo(phenylene ethynylene) derivative were applied in a near-field Kapitza-Dirac-Talbot-Lau interferometer. Although de Broglie quantum interference describes the center of mass motion of a massive body, it was shown to be sensitive to the internal molecular structure of the constitutional isomers. The different total susceptibilities of both isomers lead to different de Broglie interference shifts in the presence of external electric fields. The isomers thus become distinguishable in spite of their identical mass and chemical sum formula. Besides metrological applications, a main goal of this thesis was to synthesize model compounds for molecule interferometry to increase the preexisting mass record for quantum interferometry, which was held by the fluorofullerene C60F48 with a molecular weight of 1 633 g/mol. Near-field interferometry is a promising concept to set new records and thus to approach the quantum-to-classical transition. To meet the requirements of quantum studies with complex organic molecules in a Kapitza-Dirac-Talbot-Lau near-field interferometer – high volatility, high stability, and high molecular mass – we chose the functionalization of tetraarylporphyrins with perfluoroalkyl moieties. A modular synthesis of seven perfluoroalkyl-substituted porphyrin derivatives with up to 16 fluorous alkyl chains was presented. With this series in hand, it was possible to observe interference patterns for three of the seven derivatives. The heaviest molecule of this series for which the wave nature has been observed has a 3.3 fold higher molecular weight than the preexisting mass record for quantum interference. These experiments open a new window for quantum experiments with nanoobjects in a complexity class comparable to that of small proteins. The experimental setup of the near-field Kapitza-Dirac-Talbot-Lau interferometer is not restricted to monodisperse and pure starting compounds. It also allows for experiments with compound mixtures because individual components of compound libraries can be detected in the mass spectrometric detection unit. The preparation of porphyrin libraries gave access to compounds in a new mass region (> 10 000 g/mol). Preliminary investigations in near-field interferometers with these structures revealed suitable molecule beam properties. With these porphyrin libraries in hand, it is expected to exceed for the first time the ceiling of 10 000 g/mol for an interfering object in the future. Large, stable, highly volatile and fluorescent molecules were the goal of synthetic work that was performed for novel far-field interference experiments in a setup based on fluorescence detection. For this purpose three fluorescent fluorous phthalocyanine derivatives were prepared. With the help of a new laser-controlled micro-evaporation source it was possible to produce a beam of molecules with the required intensity and coherence. The observation of the wave nature of a free base phthalocyanine having a molecular weight of 1 299 g/mol set a new mass record for far-field molecule interferometry. The preexisting record for far-field interferometry was held by the fullerene C70 with a mass of 841 g/mol. To conclude, major contributions to the exploration of the frontiers of quantum mechanics were achieved by matter-wave interferometry using the perfluoroalkyl-functionalized molecules described in this thesis

Matter-wave interference of particles selected from a molecular library with masses exceeding 10 000 amu

The quantum superposition principle, a key distinction between quantum physics and classical mechanics, is often perceived as a philosophical challenge to our concepts of reality, locality or space-time since it contrasts with our intuitive expectations with experimental observations on isolated quantum systems. While we are used to associating the notion of localization with massive bodies, quantum physics teaches us that every individual object is associated with a wave function that may eventually delocalize by far more than the body's own extension. Numerous experiments have verified this concept at the microscopic scale but intuition wavers when it comes to delocalization experiments with complex objects. While quantum science is the uncontested ideal of a physical theory, one may ask if the superposition principle can persist on all complexity scales. This motivates matter–wave diffraction and interference studies with large compounds in a three-grating interferometer configuration which also necessitates the preparation of high-mass nanoparticle beams at low velocities. Here we demonstrate how synthetic chemistry allows us to prepare libraries of fluorous porphyrins which can be tailored to exhibit high mass, good thermal stability and relatively low polarizability, which allows us to form slow thermal beams of these high-mass compounds, which can be detected using electron ionization mass spectrometry. We present successful superposition experiments with selected species from these molecular libraries in a quantum interferometer, which utilizes the diffraction of matter–waves at an optical phase grating. We observe high-contrast quantum fringe patterns of molecules exceeding a mass of 10000 amu and having 810 atoms in a single particle

Highly Fluorous Porphyrins as Model Compounds for Molecule Interferometry

The synthesis and characterization of seven tailor-made highly fluorous porphyrin derivatives are described, as large perfluoroalkyl-functionalized organic molecules are the most complex objects for which the quantum wave nature has been observed so far. We have found, in particular, that tetrakis(pentafluorophenyl)porphyrin is a suitable starting point for a modular synthesis that is geared towards porphyrin derivatives with many peripheral fluorous chains. This allows us to tailor and optimize the sublimation features of these compounds for molecule interferometry. We have analyzed the evaporation process of one member of the series by determining the enthalpy of evaporation, as the creation of a sufficiently intense, slow molecular beam is crucial for quantum interference experiments. We present the quantum fringe pattern of a second member of the series, which we could obtain in a Kapitza?Dirac?Talbot?Lau interferometer

Single-Photon Ionization of Organic Molecules Beyond 10Â kDa

The volatilization and soft ionization of complex neutral macromolecules at low energies has remained an outstanding challenge for several decades [1]. Most volatilization techniques in mass spectrometry produce ions already in the source and most of them lead to particle velocities in excess of several hundred meters per second. For many macromolecules, post-ionization is inefficient since electronic or optical excitations can be followed by competing non-ionizing internal conversion, electron recapture, or fragmentation processes. Here, we explore the laser-assisted volatilization of neutral perfluoroalkyl-functionalized tetraphenylporphyrins as well as their single-photon ionization using vacuum ultraviolet (VUV) light at 157 nm. A systematic investigation of the ionization curves allows us to determine the molecular velocity distribution and ionization cross sections. We demonstrate the detection of single photon ionized intact organic molecules in excess of 10 kDa from a slow molecular beam

Quantum interference distinguishes between constitutional isomers

Matter waves, as introduced by de Broglie in 1923 (L. de Broglie, Nature, 1923, 112, 540),1 are a fundamental quantum phenomenon, describing the delocalized center of mass motion of massive bodies and we show here their sensitivity to the mol. structure of constitutional isomers. [on SciFinder(R)

Laser-Induced Acoustic Desorption of Natural and Functionalized Biochromophores

Laser-induced acoustic desorption (LIAD) has recently been established as a tool for analytical chemistry. It is capable of launching intact, neutral, or low charged molecules into a high vacuum environment. This makes it ideally suited to mass spectrometry. LIAD can be used with fragile biomolecules and very massive compounds alike. Here, we apply LIAD time-of-flight mass spectrometry (TOF-MS) to the natural biochromophores chlorophyll, hemin, bilirubin, and biliverdin and to high mass fluoroalkyl-functionalized porphyrins. We characterize the variation in the molecular fragmentation patterns as a function of the desorption and the VUV postionization laser intensity. We find that LIAD can produce molecular beams an order of magnitude slower than matrix-assisted laser desorption (MALD), although this depends on the substrate material. Using titanium foils we observe a most probable velocity of 20 m/s for functionalized molecules with a mass m = 10'000 Da

Electric moments in molecule interferometry

We investigate the influence of different electric moments on the shift and dephasing of molecules in a matter wave interferometer. Firstly, we provide a quantitative comparison of two molecules that are non-polar yet polarizable in their thermal ground state and that differ in their stiffness and response to thermal excitations . While C 25 H 20 is rather rigid, its larger derivative C 49 H 16 F 52 is additionally equipped with floppy side chains and vibrationally activated dipole moment variations. Secondly, we elucidate the role of a permanent electric dipole moment by contrasting the quantum interference pattern of a (nearly) non-polar and a polar porphyrin derivative. We find that a high molecular polarizability and even sizeable dipole moment fluctuations are still well compatible with high-contrast quantum interference fringes. The presence of permanent electric dipole moments, however, can lead to a dephasing and rapid degradation of the quantum fringe pattern already at moderate electric fields. This finding is of high relevance for coherence experiments with large organic molecules, which are generally equipped with strong electric moments

Real-time single-molecule imaging of quantum interference

The observation of interference patterns in double-slit experiments with massive particles is generally regarded as the ultimate demonstration of the quantum nature of these objects. Such matter–wave interference has been observed for electrons, neutrons, atoms and molecules and, in contrast to classical physics, quantum interference can be observed when single particles arrive at the detector one by one. The build-up of such patterns in experiments with electrons has been described as the “most beautiful experiment in physics”. Here, we show how a combination of nanofabrication and nano-imaging allows us to record the full two-dimensional build-up of quantum interference patterns in real time for phthalocyanine molecules and for derivatives of phthalocyanine molecules, which have masses of 514 AMU and 1,298 AMU respectively. A laser-controlled micro-evaporation source was used to produce a beam of molecules with the required intensity and coherence, and the gratings were machined in 10-nm-thick silicon nitride membranes to reduce the effect of van der Waals forces. Wide-field fluorescence microscopy detected the position of each molecule with an accuracy of 10 nm and revealed the build-up of a deterministic ensemble interference pattern from single molecules that arrived stochastically at the detector. In addition to providing this particularly clear demonstration of wave–particle duality, our approach could also be used to study larger molecules and explore the boundary between quantum and classical physics